Hobart's Paulo de Souza, the only scientist in the southern hemisphere who has an active involvement in the mission, said Opportunity had confirmed that watery above-freezing conditions had existed in the region about 3.7 million years ago.

"If there was ever life on Mars, then this would have been the mud for it to live in," he said.

Professor de Souza joined NASA's Spirit and Opportunity rover missions after he, along with colleagues at Germany's Johannes Gutenburg University, successfully shrunk washing machine-sized Mossbauer spectroscopy technology to the size of a computer mouse, small enough to be flown to Mars.

Originally from Brazil, he then moved to Hobart to work with the CSIRO and the University of Tasmania.

His latest project with the CSIRO in Hobart has involved gluing tiny radio transmitters on to the backs of bees.

Prof de Souza will today cut an Opportunity rover birthday cake and speak to a packed auditorium, at the CSIRO's Canberra Discovery Centre.

He still plays an active role in the mission's planning, supervision of the rover's equipment, and the interpretation of data.

Prof de Souza said the NASA team had been surprised when Opportunity and Spirit both exceeded their three-month life expectancies in 2004.

It hoped Opportunity would kick on for at least another two years.

"The most productive time of the mission is now because we are in a special place at the crater ... a scientific paradise" he said.